Prostate cancer (PCa) has major impacts on veterans' health care and its incidence will continue to grow as the population ages. Despite continual progress in the development of PCa therapies, patients with androgen-deprivation-therapy (ADT)-resistant disease have limited options. Perenteral estrogens with reduced cardiovascular toxicities have shown promise in PCa treatment in recent years. An orphan G protein-coupled receptor (GPR30) with high-affinity and low-capacity binding to estrogens was identified at both the plasma membrane and the endoplasmic reticulum. This receptor is believed to be the key mediator of the non-genomic action of estrogens. Upon its binding to ligand, GPR30 either stimulates or inhibits cell proliferation in an ER- independent, cell type-specific manner. The identificaion of G-1 (1-[4-(6-bromobenzo[1,3]dioxol-5yl)-3a,4,5,9b- tetrahydro-3H-cyclopenta[c]quinolin-8-yl]-ethanone) as a GPR30-selective agonist with no estrogenic activity provides a unique opportunity to elucidate the biological significance of GPR30 in cell growth regulation, especially in cells that express ER1 and/or ER2. Using G-1, and confirmed by siRNA knockdown experiments, we recently demonstrated strong inhibitory effects of G-1 on the growth of AD and ADT-resistant PCa cells in culture. It also inhibited PC-3 xenograft growth in nude mice. A trend of reduction of GPR30 mRNA expression was observed in PCa clinical specimens when compared to their adjacent normal tissues although the degree of expression varies a great deal among PCa specimens. Treatment of PCa cells with 5-aza-2'-deoxycytidine, a demethylating agent, tricostatinA, a HDACi, or an ADT increased GPR30 expression. Based on these novel findings, we here hypothesize that activation of GPR30 signaling via its specific ligand G-1, either alone or in combination with a demethylating agent, a histone deacetylase inhibitor (HDACi), or androgen ablation, is an effective anti-PCa therapy, and that GPR30 has prognostic value in PCa. Three aims are proposed to test this hypothesis. Objective 1: Establish the role of GPR30 in G-1-induced growth inhibition/cell kill in AD and ADT- resistant PCa cells under in vitro and in vivo settings. Objective 2: Determine whether DNA methylation, histone deacetylation, or androgen repression are involved in the regulation of GPR30 expression and compare the efficacies of G-1, alone or in combination with one of these agents in curbing PCa growth. Objective 3: Evaluate the prognostic value of GPR30 expression in PCa. This project will provide the first evidence in support of GPR-30 as a novel PCa therapeutic target and lay down a foundation for future development of GPR30-based therapies for PCa.